Chelsea college to a sentry-box, phr. — Green’s Dictionary of Slang

Chelsea college to a sentry-box phr.

also Chelsea Hospital to a sentry-box

[Chelsea College, the second London Polytechnic, was founded in 1891. It orig. contained the Chelsea Art School]

the longest possible odds.

1819		‘One of the Fancy’ Tom Crib’s Memorial to Congress 38: All Lombard-street to nine-pence on it. Note. More usually Lombard St. to a china orange. There are several of these fanciful forms of betting – Chelsea College to a sentry-box; Pompey’s pillar to a stick of sealing-wax, etc. etc [F&H].
1891		Lic. Vict. Mirror 30 Jan. 7/2: Tom’s hit the opening round, and led Aaron’s friends to call out in their jubilation: ‘It’s all your own, my boy; Chelsea Hospital to a sentry-box.’ [F&H].